1) Field of the Invention
The present invention relates to duct dampers, and more particularly to a sound absorbing duct damper capable of providing a variable restriction to a gas flowing through a duct.
2) Description of Prior Art
The subject matter of the present invention is going to be described in relation to an air duct. However, it is considered to be within the scope of this invention that this invention could be used in ducts within which flow other types of gases. It is not considered possible to use the present invention within liquid flowing ducts.
Ventilation in homes and buildings requires that air be circulated and distributed according to the requirements of the different parts of the home or building. The airflow into a room of a home or building depends upon (1) it's proximity to the source of the airflow, (2) the cross-sectional area of the ventilation duct connecting to the room and (3) the position of the room relative to the sun (whether the sun gets the afternoon sun or the morning sun). The flow rates of air into different rooms are controlled by way of dampers. These dampers are installed within the duct work. The dampers are used to vary the airflow to each individual room so that each room of the home or building receives the desirable amount of heating or cooling.
When a home or building is being constructed, an air conditioning contractor installs the duct work, and at the same time installs the damper at the particular location within the duct work. Typically, the damper is fabricated at the site. Fabrication occurs by the air conditioning contractor cutting a section of sheet metal which somewhat conforms to the interior of the duct so that if this section of sheet metal is located precisely transverse within the duct, the airflow will be substantially closed. This section of sheet metal is mounted on a pair of diametrically lined fasteners with each fastener to protrude through a hole in the sidewall of the duct. Movement of this section of sheet metal is controlled by physically pivoting of the fasteners on which the sheet metal is mounted which will cause this section of sheet metal to move to various angular positions within the duct. If this section of sheet metal is positioned in substantial axial alignment within the duct, essentially no restriction of the airflow occurs.
This type of fabrication of a damper has many disadvantages. The fabrication procedure is quite time consuming. Air conditioning contractors are normally paid between twenty-five and fifty dollars an hour, and if it takes a couple of hours to manufacture and install such a damper, then that damper becomes quite expensive. Also, such fabricated type of dampers frequently "chatter" as the air is moved past the damper. This "chatter" is caused by the rush of air past the damper causing the damper to vibrate. This vibration produces a high-pitched sound which is exceedingly undesirable to most people.
Also, the installation procedure of such a fabricated damper is rather difficult and also a time consuming procedure. Many times the fabrication produces a section of sheet metal that just doesn't quite fit within the duct, either being too tight, which requires modification, or it's too loose which is not capable of completely restricting of the airflow if total air restriction is desired. Also, such fabricated type of dampers do not adjust easily and frequently bind during the adjusting process.